The present invention relates to a method and apparatus for gravel packing, frac packing or other treatment of a production zone and more particularly for gravel packing, frac packing or other treating of multiple production zones with one trip of the apparatus into the well.
During the production of hydrocarbons from a well, loose sand and degraded sandstone migrate into the wellbore as the formation deteriorates under the pressure and flow of fluids. This migration of particles may eventually clog the flow passages in the well. One method of controlling migration into a wellbore is the placing of a pack of gravel on the exterior of a perforated or slotted liner or screen which is positioned across from the producing formation to present a barrier to the migrating sand while permitting hydrocarbon flow. The gravel is carried to the formation in the form of a slurry, the carrier fluid being removed and returned to the surface. The gravel is packed around an inner liner or screen which maintains the gravel around the exterior of the screen and the slurry fluid enters the liner or screen from its exterior for flow back to the surface or is forced into the formation.
In a typical gravel packing operation, a liner assembly having a perforated liner or screen is disposed within a perforated casing and positioned adjacent the formation. A packer is set above the zone between the liner and the well casing. A tubing string is run inside the liner assembly at the area of the zone. Gravel slurry is pumped down the tubing string and through a crossover tool and out into the annulus between the liner and the casing below the packer at a suitable location above the zone where it descends and the gravel is deposited in the area of the screen as the carrier fluid passes through the screen. The crossover tool routes the upward movement of the returning fluid back outside the liner assembly, the fluid then traveling up to the surface. Once a pressure build up is noted at the surface, the flow of gravel-laden fluid is stopped. After the gravel packing is completed, the tool is generally moved and the circulation of fluid is reversed, a clean fluid being pumped down the casing annulus and back up the tubing in order to flush out sand remaining in the tubing. Subsequently, the well may be subject to other treatments, if necessary, and produced. One such treatment may be fracturing the well. Patents disclosing different methods of gravel packing include U.S. Pat. Nos. 3,710,862; 3,952,804; and 4,044,832.
In gravel packing wells having multiple production zones, it is desirable to utilize a method and apparatus which has the capability of gravel packing the multiple zones in a single trip into the well. See for example, U.S. Pat. Nos. 4,105,069 and 4,270,608.
Some prior art methods and apparatus for gravel packing multiple zones require that the operating string trip into the well for each producing zone. The outer string, containing the packing screens, are assembled from the bottom up in a step by step process and then the operator must withdraw the operating string between zones in order to add components to the outer string. This also renders it impossible to pack an upper zone before a lower zone, or to set or inflate packers in any order other than the lowest packer first. Because of the order in which the zones are packed, it is almost impossible to repack zones below the uppermost zone. In some instances, this is due to an inability to place the operating string back in the desired location, due to restrictions placed in the outer string after packing a zone. In other cases it is due to an inability to relocate the desired zone and to position the gravel ports with any precision.
A conventional multi-zone packing system includes an outer completion string having a production packer with slips for supporting the completion string within the cased well. Disposed below the production packer is an upper closing sleeve and an upper zone screen. An isolation packer is disposed below the upper zone screen and a lower closing sleeve and a lower zone screen which are disposed below the isolation packer. A first seal bore is disposed between the production packer and upper closing sleeve and a second seal bore is disposed between the upper closing sleeve and upper zone screen. A third seal bore is disposed between the upper zone screen and isolation packer and a fourth seal bore is disposed at the lower zone screen. A sump packer is disposed below the lower zone screen around a lower seal assembly. In the case of an open hole, inflatables would be used in place of the sump packer and isolation packers. An inner service tool includes a plurality of seal units forming an outer conduit and an inner center tube. The center tube and seal units form an annulus extending from upper ports in the uppermost seal unit to lower crossover ports extending through the outer conduit formed by the seal units and center tube. An additional length of seal units extends from the crossover ports downwardly for several feet followed by an extension and an additional set of seal units to a ported sub and lower seal assembly at its lower end. To be able to open and close the closing sleeves, the service tool includes at least two shifting tools, one above the crossover tool and one below. A single shifting tool may be used but it must be located very close to the gravel pack ports so that the shifting tool can be raised a very short distance, close the closing sleeve, and still have the gravel pack ports within the short distance range. An upper ball check is provided at the lower terminal end of the center tube to prevent downward flow through the flowbore of the center tube. A lower check valve is provided in the conduit of the seal units to prevent the downward flow of fluids in the annulus and into the flowbore formed by those seal units disposed below the crossover ports. Another ball check valve is provided at the lower terminal end of the seal units.
In operation, the sump packer is lowered into the well and set by a wire line at a predetermined location in the well below the zones to be produced. The completion string is then assembled at the surface starting from the bottom up until the completion string is completely assembled and suspended in the well up to the packer at the surface. Then, the inner service tool is assembled and lowered into the outer completion string. The service tool includes one or more shifting tools, depending upon the number of production zones, for opening and closing the closing sleeves. When the service tool is lowered into the completion string, the shifting tool opens all of the closing sleeves in the completion string. Therefore, it does not matter whether the closing sleeves were initially in the open or closed position since the shifting tools will move them all to the open position as they pass downwardly through the completion string. These sleeves later must be moved to the closed position to set the isolation packer. The packer assembly and setting tool are then attached to the upper ends of the service tool and completion string and the entire assembly lowered into the well on a work string onto the sump packer. Upon aligning the zone screens with the production zones, the production packer is set to suspend the completion string within the cased well.
In gravel packing the lower production zone, the setting tool is disconnected from the completion string and is raised such that the set of upper seals no longer engages the first seal bore of the production packer. At that time, the seals on the upper seal units sealingly engage the first, third, and fourth seal bores and the crossover ports are adjacent the lower closing sleeve which is open. In order to set the isolation packer, the lower closing sleeve must be closed utilizing a shifting tool in the service string so that the annulus between the closing sleeve and the outside of the service tool may be pressurized to set the isolation packer.
Gravel slurries are then pumped down the flowbore of the work string and center tube. The ball check valve directs the gravel through the crossover ports and through the open lower closing sleeve and into the lower annulus. The gravel builds in the lower annulus adjacent the sump packer with the returns flowing through the lower zone screen and ported sub. The returns flow up the flowbore of the lower seal units and through the lower ball check valve. The returns then pass through the bypass apertures around the crossover ports and up the annulus. The returns thereafter flow out through the upper ported sub and up the upper annulus formed by the work string and outer casing. Upon completing the gravel pack of the lower production zone, fluids are reverse circulated down to the crossover ports. Fluid is then pumped down the annulus between the work string and casing, through the upper ported sub at the upper end of the seal units, down the annulus, and through the bypass apertures around the crossover ports. The lower ball check prevents the fluid from passing down into the flowbore of the lower seal units and directs the flow through upper ball check and flowbore to the surface.
In gravel packing the upper production zone, the service tool is raised such that the crossover ports are adjacent the upper closing sleeve. Also, the seals on the seal units sealingly engage the first, second, and fourth seal bores. Circulation and reverse circulation occurs substantially as previously described with respect to the lower production zone.
In a gravel pack operation for three or more production zones, upper and lower shifting tools are used with one of the shifting tools being in the service tool and the other in the wash pipe. The shifting tools on the service tool push the closing sleeves to the down or open position as they pass through the completion string. Then, the upper shifting tool is raised through the upper closing sleeve to pull the upper closing sleeve to its upper or closed position. Once the upper closing sleeve has been closed, the gravel pack ports are placed in position to pressure up the annulus and set the isolation packer. This procedure requires that the service tool be raised and then lowered back down to reopen the sleeve but not lower the upper shifting tool through the closing sleeve. This creates a lot of movement up and down to get the closing sleeve in the proper position.
In a gravel pack operation for a dual zone, it is possible to use only one shifting tool. However, in utilizing only one shifting tool, it is necessary to space the shifting tool very close to the gravel pack ports such that the shifting tool can be raised through the closing sleeve to pull the sleeve closed and yet not raise the gravel pack ports so high that the gravel pack ports are moved above the seal bore of the isolation packer so as to prevent pressuring up to set the isolation packer. This requires a very short reciprocal motion thereby requiring that the service string be spaced out very accurately with respect to the completion string. Another problem with locating the closing sleeve and shifting tool so close to the gravel pack ports is that the gravel pack sand tends to get into and around the keys of the shifting tool, locking up the keys so that they will not function properly. Further, the use of a single shifting tool is useful for relatively shallow, straight wells. However, when gravel packing deep wells or highly deviated wells where the pipe making up the work string has high movement, the operator has difficulty knowing whether the gravel pack ports are properly positioned adjacent the closing sleeve.
Another disadvantage of the prior art is that the prior art method and apparatus does not permit performing the gravel pack in a weight-down position which is preferred in the industry. The work string is made up of steel tubing which will contract and expand in the well, particularly when the work string is several thousand feet long. At such lengths, the steel stretches causing the lowermost end of the work string to move several feet within the well. This is particularly a problem in gravel packing operations when it is necessary to position the gravel pack ports accurately across from the closing sleeves.
It is also advantageous to perform other operations, such as hydraulic fracturing, in a weight-down position. The work string extending from the top of the service tool to the surface has substantial movement during a fracturing or fracpac operation. The movement of the work string is even more exaggerated than during a gravel pack operation due to the thermal effects caused by the cool fracturing fluid being pumped down through the work string at a very high rate. This tends to cause shrinkage in the work string. Further, the work string tends to balloon due to the increased pressure within the work string which also causes the work string to shrink. These combined affects tend to shorten the work string substantially during the operation.
Although a weight indicator is used at the surface to determine the amount of weight hanging off the crown block, the fact that the weight appears to be staying the same does not provide an indication as to whether the length of the work string is changing at its lower end. If the work string shrinks several feet, the gravel pack ports may be raised a distance so as to cause the gravel pack ports to be moved up into the packer seal bore and prematurely end the operation.
Another problem during the frac pack operation is that the pumping of the fluid through the work string at a very high rate causes a vibration in the work string thereby causing it to move up and down. With a very long work string, this reciprocable motion may get very large causing it to bounce up and down within the well such that it may act like a spring.
The present invention overcomes the deficiencies of the prior art.